Preparation of a target specific fraction controlling the proliferation of granulocytes. The abolishment of the specificity by glutathion.

A low molecular weight fraction (GI-3) was prepared from peripheral horse blood leukocytes. This fraction inhibits the proliferation of bone marrow cells, the effect is dose dependent. The proliferation of thymocytes and HeLa cells is not affected by GI-3. This specificity was abolished when glutathion was applied together with GI-3; the 3H-TdR uptake of thymocytes in vitro was completely inhibited, however, slight or no effect was observed on bone marrow and HeLa cells, respectively.